I logged into the router via a pc and same problem (in Ffx, the WPS setting isn't shown; in Chrome it showed, but changing it and hitting Apply/Save didn't have any effect).
I did figure out a way round it, in case anyone comes here looking for a solution to the same problem.
Here's how you turn WPS off: 1. Click on the 'Maintenance' tab.
2. Under System -- Backup Settings click the 'Backup Settings' button.
This will download your routers config file to your hard drive (whatever your default downloads folder is).
3. Open the file with a plain text editor (if you're a terminal fan, vi or emacs will do. If not, Tincta is a great one to use on macs. Sorry, I don't know what you Windows folks use. Notepad?).
4. Search the file for WPS and change the <Enable> setting from 'TRUE' to 'FALSE',
It should look something like this:
<WPS>
<Enable>FALSE</Enable>
5. Save the file.
6. Go back to the Maintenance page, and under 'System --Update Settings' hit 'Choose File'.
7. From the dialog, choose the file in your downloads folder that you just edited. Then click 'Update Settings' on the router page.
Wait a couple of minutes for it to update and reset, and you 're done.